Conventionally, to supply a product just after manufacturing from a stock position to a work position and to stock the product at another position after working are automated by a product supply unit.
Conventional product supply units are explained below, referring to FIGS. 1 and 2.
FIG. 1 is an illustration showing the principle of operation in an example of conventional product supply unit. As shown, the conventional product supply unit uses pick and place mechanisms (hereinafter referred to as `P/P mechanism`) 101, 102 where a cam or ball screw and a slide mechanism are combined. In conducting the supply operation or stock operation of a product by these mechanisms, by reciprocating a product holding nozzle, the product is supplied from a supply-side product receiver 110 to a product processing position 100, or is supplied from the product processing position 100 to a stock-side product receiver 210.
FIG. 2 is an illustration showing the principle of operation in another example of conventional product supply unit disclosed in Japanese patent application laid-open No. 62-79136 (1987). In this example, a link mechanism is used. With this link mechanism, where a support 520 is disposed between members 510 and 500 attached to rotational center shafts 511 and 501, respectively and coupling shafts 512, 502 compose a pair of parallel links, the rotational center shaft 512 is rotated by a driving motor 530 through a power transmission belt 540, thereby picking up a product 560 from a magazine 550 disposed at the lowermost position of the support 520, further rotated to supply it to carrier roller 570 side.
However, in the conventional product supply unit in FIG. 1, there is a problem that the operation time is long. The first reason is that, since the supply and stock of product is conduct by the reciprocating operation and therefore only the product holding nozzle returns on the return way while conducting the lost motion with no supply and stock of product, the operation time is wasted by that much. The second reason is that in the supply operation, the up/down motion of the product holding nozzle for holding the product at the supply-side receiver 110 and the up/down motion of the product holding nozzle at the product processing position 100, and in the stock operation, the up/down motion of the product holding nozzle at the stock-side product receiver 210 are all alternately performed, therefore the operation time is consumed in each of the motions.
Also, in the conventional product supply unit in FIG. 2, there is a first problem that the rotation operation lacks smoothness. The reason is that, when the pair of links align at the uppermost and lowermost positions of the support, the dead point, which is the worst weakness of link mechanisms, occurs and the rotation operation is thereby obstructed. Also, there is a second problem that the precision is significantly lowered at the work position that is assigned to the lowermost position of the support. The reason is that the dead point occurred causes the most unstable structure state of the link mechanism.
On the other hand, the product supply unit may be also used to automate the electrical characteristic test or burn-in test of a semiconductor product. For example, in case of electrical characteristic test, the product is supplied from the supply tray to the contact pin on the measurement box of IC tester, then measured while being pressed at a given contact pressure. After the measurement, the product is selected and stocked at a given place based on the test result. Thus, from the supply until stock of the product, it is automatically conveyed by the product supply unit.
The measurement box where the IC tester and the measured product are mounted has been scaled up with the recent functional enhancement of semiconductor product. For example, when the P/P mechanism is simply used, a stocker (tray elevator) 701 for the supply or stock of a product 700, as shown in FIG. 3, needs to be disposed at the circumference in the plane direction of a measurement box 702 due to the stock amount. Therefore, the distance between the stocker 701 and a measurement contact 703 becomes long and the operation time taken between the stocker 701 and the measurement contact 703 becomes long. Also, the floor area occupied by the unit is large. To shorten the operation time, it can be thought that multiple carrier mechanisms are provided such that they relay the distance between the stocker 701 and the measurement contact 703 and the moving distance assigned to each carrier mechanism is shortened, and the moving speed in the horizontal direction of each carrier mechanism is speeded up. In this case, each carrier mechanism may include not only the P/P mechanism but also a carrier mechanism using a rotary table. However, in such unit composition, the cost of unit must be increased since the number of components increases. Also, there is a problem that the floor area occupied by the unit remains large and thus the outer area of the unit cannot be decreased.
To solve this problem, there is a technique that the stocker 701 is, as shown in FIG. 4, overlaid on the measurement box 702 and a tray 704 is taken out from the bottom of the stocker 701 to supply or stock the product 700 through the tray 704. However, even in this case, the outer area of the unit cannot be decreased since the stage area for mounting the tray 704 to be taken out from the stocker 701 is necessary.
So, as shown in FIG. 5, to realize a mechanism that the product 700 is supplied and stocked directly between the tray 704 on the top of the stocker 701 overlaid on the measurement box 702 and the measurement contact 703 is most effective for shortening the operation time and for decreasing the outer area of unit. In such composition, it is necessary to move the product a distance along the drop height from the top of the stocker to the measurement box lying under the stoker. Hereupon, when the P/P mechanism is used for this transportation, the product is, at a stroke, moved the distance along the drop height by the single mechanism. Therefore, the operation distance for the single mechanism becomes long and the operation time on the forward way becomes very wasteful. Also, when the rotary link mechanism in FIG. 2 is used instead of the P/P mechanism, the position precision of product is significantly lowered at a position where the product support comes to the measurement point at the lowermost, thereby causing an error in measurement.